T cell receptors recognize peptide antigens bound to and presented by the major histocompatibility complex (MHC) in a highly specific manner. A unique class of ligands called superantigens (SAgs), which are a type of toxin secreted by bacteria, bind to the T cell receptor in a different manner than normal antigens. When a foreign antigen enters the immune system, T cell receptors are activated and the normal response activates a small percentage of the immune system, less than 0.01 percent. In comparison, these toxins can activate up to 30 percent of the immune system. This overstimulation of the immune system leads to a massive release of cytokines such as TNF-a and IL-2, thereby causing severe inflammatory reactions. Though these toxins have been identified as the cause of Toxic Shock Syndrome and linked to other diseases, in recent years these toxins have increasingly been implicated in several pulmonary and cardiovascular diseases. Necrotizing pneumonia is among these diseases, which can involve airway inflammation, permanent airway destruction, and mortality. Most importantly for the present application, studies have shown that these exotoxins contribute directly to severe lung infection caused by Community- Associated Methicillin-Resistant S. Aureus (CA-MRSA). The increase in prevalence of MRSA, both in hospitals and the community, emphasizes the immediate need to target the toxins secreted by this bacterium. Therefore, in this application, T-cells will be engineered against these exotoxins. The exotoxins that will be focused on include Staphylococcal enterotoxin B (SEB), Staphylococcal enterotoxin C3 (SEC3), and toxic shock syndrome toxin 1 (TSST-1). The approach is to use a novel method of directed evolution to engineer T cell receptors that bind with high affinity to these clinically important toxins. Soluble forms of high affinity T cell receptors can neutralize the systemic toxicity of the SAgs, as has been recently shown in animal models with the toxin SEB. PUBLIC HEALTH RELEVANCE: The long-term goal of this application is to engineer soluble T cell receptors to treat exotoxin-induced pulmonary disease. To accomplish this goal, the first specific aim is to design, engineer, and express T cell receptors that bind with high-affinity to the SAg exotoxins SEC3 and TSST-1. The second aim of this application is to characterize and evaluate the anti-toxin efficacy of the soluble T cell antagonist proteins in vitro and in pulmonary disease animal models.